Conventionally, an advective accumulation method has been known as a method for accumulating fine particles two-dimensionally or three-dimensionally at a high density on a substrate. The advective accumulation method is a method for dipping, in a dispersion liquid of particles dispersed for a long period of time in a solvent such as an aqueous solution, a flat substrate, such as glass, which has a strong affinity for the solvent and thereby producing a particle film on the substrate. This method achieves high-density accumulation of the particles through utilization of autonomous accumulating force of the particles at the interface between the substrate and the dispersion liquid. A dip coater has been mainly used so far for the formation a particle film by the advective accumulation method (e.g., see Non-patent Literature 1).
With a dip coater, a fine-particle film is formed on a substrate by, after dipping the substrate in a fine-particle dispersion liquid, withdrawing the substrate from the fine-particle dispersion liquid at a given speed. It should be noted here that during the withdrawal of the substrate from the fine-particle dispersion liquid, there appears a meniscus between the substrate and the fine-particle dispersion liquid, whereby the nanoparticles are supplied toward the edge of the meniscus by a liquid current and capillary force. Because the solvent evaporates in the meniscus area, a decrease in thickness of the liquid film in relation to the film thickness of the particle film causes liquefaction bridging force between the particles, whereby the nanoparticles are immobilized on a surface of the substrate.
Further, there have been reports on a method for producing a particle film by a polystyrene particle dispersion liquid with use of a horizontally-driven nanocoater (e.g., see Non-patent Literatures 2 and 3). Specifically, there is disclosed a method for forming a particle film by inclining a second substrate at 0.14° to a first substrate, interposing therebetween a suspension containing nanoparticles, and moving only the first substrate in a horizontal direction.